Device for osteosynthesis

ABSTRACT

A device of performing osteosynthesis includes an osteosynthesis element, e.g., a bone plate, having an upper face, a lower face and an opening with a central axis linking the upper and lower faces. The opening receives a multi-axial pivotable insert for a longitudinal bone fixing element, such as a bone screw. The insert has a central passage with a longitudinal axis for housing the bone fixing element. The insert may be configured as a helical spring with an external sheath surface and an internal sheath surface that defines the central passage. When placed in the through hole, the insert is rotationally fixed relative to its longitudinal axis, but remains pivotally adjustable within the through hole relative to the osteosynthesis element.

RELATED APPLICATION DATA

The present application is a continuation of the U.S. National Stagedesignation of co-pending International Patent Application No.PCT/CH2002/000673, filed Dec. 6, 2002, the entire content of which isexpressly incorporated herein by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a device for osteosynthesis and, moreparticularly, to a device having a polyaxial insert for receiving alongitudinal bone fixation element, such as a bone screw, for securingthe device to a bone.

BACKGROUND OF THE INVENTION

Devices of the present type are used for a polyaxial, rigid screwconnection, particularly in the region of the spinal column, for examplefor pedicle screws or pedicle hooks. However, they can also be usedgenerally for plate osteosynthesis. In addition, uses for externalfixators as well as for intervertebral implants are also possible.

Such a device is already known from U.S. Pat. No. 6,235,003, in which apivotable, ring-shaped insert is present between the screw head and thebore of the bone plate, which insert can be compressed and expanded bymeans of a slit, in order to thereby achieve improved fixation betweenscrew and plate. The disadvantages of this known device are multiple.The axially rigid insert, configured to be circular, can turn with thescrew as it is turned, and thereby prevents locking. Moreover, theinsert can also twist completely within the plate bore, so that it thencomes to rest with the wrong side up (inner cone narrows in the wrongdirection).

The above discussion of the state of the art takes place merely toexplain the surrounding field of the invention, and does not mean thatthe cited prior art was actually published or publicly known at the timeof this application or its priority.

SUMMARY OF THE INVENTION

The present invention is intended to alleviate the problem discussedabove. The invention is based on the problem of creating a device forosteosynthesis in which the longitudinal bone fixation elements(explained in greater detail in the following, using the example of bonescrews) are polyaxially movable relative to the bone plate and can belocked at a stable angle, and which device requires a total of only fourdesign elements, namely a bone plate, an insert for the hole in theplate, a longitudinal bone fixation element (e.g. bone screw), and aturning instrument (e.g. a screwdriver).

As compared with U.S. Pat. No. 6,235,033, the invention possesses theadvantage that no additional spreading screw is required. It is alsoadvantageous that the helical spring, which is axially compressible andexpandable due to its nature, is also radially compressible andexpandable, at the same time. Furthermore, production is simplified andless expensive. The helical spring furthermore has the advantage thatwhen a bone screw is screwed in, the head of the bone screw, which ispreferably configured to be conical, wedges itself into the interior ofthe helical spring.

In a preferred embodiment, the windings (preferably two or morewindings) of the helical spring are configured to be non-round. In thefollowing, “non-round” means any cross-section that deviates from aprecisely round area, particularly prismatic and ellipticalcross-sections. The cross-section of the passage that stands orthogonalto the central axis is also preferably configured to be non-round. Inthis connection, it is advantageous if the cross-section of the outersheath surface that stands orthogonal to the longitudinal axis has ashape that essentially corresponds to the cross-section of the passage.In this way, the additional advantage can be achieved that the insertcannot rotate about its own axis while the bone screw is being screwedin. This is because the latter would have the result that no relativemovement would take place between the insert and the screw any longer,so that spreading open of the insert would no longer be possible, andtherefore locking of the screw would also not be possible.

Rotation-locking of the insert in the passage can be achieved not onlyby means of a corresponding geometry of the passage and the insert, butalso with other means that have the result that the insert is mounted inthe passage so as to prevent rotation relative to its longitudinal axis,as long as only the insert remains at least partially axiallydisplaceable relative to the osteosynthesis element, and preferablypivotable, within the passage. For example, it is already sufficient ifthe helical spring is attached in the passage at least at one point ofits spring helix (e.g. at one of its free ends).

In a particular embodiment, the cross-section of the passage in theosteosynthesis device preferably configured as a bone plate isconfigured to be polygonal, preferably hexagonal, so that the passagerepresents a prism, preferably a hexagonal prism. The helical springthen advantageously also has a polygonal (e.g. hexagonal) cross-section.In the hexagonal embodiment, the bone screw can be pivoted in threeplanes, at the same time, in the hexagonal passage, so that any desiredpivot angle can be set. This is only limited by the plate thickness andby the contact of the insert with the narrowing in cross-section that ispreferably made. In the case of most bone plates, of course, severalpassages are present.

In another embodiment, the passage of the osteosynthesis element widensat least in the direction of one of its two exit openings, preferablyconically. The passage of the insert is typically configuredprismatically, preferably as a hexagonal prism. However, it can also beconfigured as a hollow circular cylinder.

In another embodiment, the diameter of the central bore of the insert isnarrowed in one direction, and the bore is preferably configured as acone. This configuration allows spreading of the insert by means of acounter-cone, i.e. for example with a bone screw that has a conicalscrew head. However, the bore of the cylinder can also be configured asa circular cylinder.

The cross-section of the passage that stands orthogonal to the centralaxis, in the osteosynthesis device preferably configured as a boneplate, can also be configured to be elliptical.

It is practical if the surface of the insert is roughened, e.g. blastedto be rough, preferably in the region of its outer sheath curve.Accordingly, the passage in the bone plate can also be roughened, e.g.blasted to be rough. The passage can then be provided with amicrotexture, in corresponding manner, e.g. in the form of grooves thatrun peripherally on the circumference. The advantage of this embodimentlies in the positive-lock connection between insert and bone plate thatis achieved thereby.

The surface of the insert can be provided with a coating of a hardermaterial than the insert, preferably in the region of its outer sheathcurve, and possibly be additionally provided with a macrotexture. Thepassage of the osteosynthesis element can also be roughened up,preferably blasted to be rough. The passage of the osteosynthesiselement can be provided with a coating of a harder material than that ofthe osteosynthesis element.

In another special embodiment, the passage in the osteosynthesis device,preferably configured as a bone plate, narrows towards the lower faceand preferably also towards the upper face, so that a narrowing incross-section results, which prevents the insert from falling out orbeing pressed out. It is practical, in this connection, if thecross-sectional narrowing of the passage and the compressibility of theinsert are coordinated with one another, in such a manner that theinsert, configured as a helical spring, can be introduced into thepassage by means of a temporary reduction of its largest diameter.

In a particular embodiment, the outer sheath surface of the insert isconvex, and the passage of the osteosynthesis element is configured tobe concave.

It is advantageous if the osteosynthesis device, at least in the regionof its passage, and the insert, at least in the region of its outersheath curve, consist of different materials, preferably those havingdifferent hardness. The insert, for example, can consist of abiocompatible plastic, and the osteosynthesis device (e.g. a bone plate)can consist of a body-compatible metal. However, the insert can also bemetallic, and the device can be made of a plastic, preferably areinforced plastic. The different materials result in plasticdeformation of the surface and therefore in a positive lock.

The height of the insert should be smaller, measured in the direction ofits longitudinal axis, than the height of the passage in the bone plate,measured in the direction of its central axis. Advisably, the height ofthe insert range of 40%-85%, preferably 45% to 65% of the height of thepassage.

The bone screws that serve for introduction into the insert preferablyhave a conical screw head, which additionally can be provided with anoutside thread. The advantage of this configuration lies in the factthat spreading and locking of the insert in a single step is madepossible.

In a particular embodiment, the diameter of the spring wire of thehelical spring is smaller than or equal to the distance between twothread crests of the outside thread of the screw head. The cross-sectionof the spring wire of the helical spring can also be non-round,preferably square or diamond-shaped.

The pitch of the windings of the helical spring should advantageouslycorrespond essentially to the pitch of the outside thread of the screwhead. The diameter of the spring wire of the helical spring shouldfurthermore advantageously be greater than the radial cross-sectionalnarrowing of the passage.

The invention and further developments of the invention will beexplained in greater detail in the following, on the basis of therepresentations, some of them schematic, of several exemplaryembodiments. Analogous applications for pedicle screws, pedicle hooks,external fixators, or intervertebral implants are possible.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 shows a perspective representation of a device forosteosynthesis, implemented in the form of a bone plate;

FIG. 2 shows a cross-section through the bone plate of FIG. 1, with aninsert in the form of a helical spring;

FIG. 3 shows a cross-section taken along the line III-III in FIG. 2;

FIG. 4 shows a diagrammatic, perspective view of an insert in the formof a hexagonal helical spring;

FIG. 5 shows a perspective representation of the bone plate of FIG. 1,with the insert shown in FIG. 4; and

FIG. 6 shows a longitudinal section through a bone screw for the devicefor osteosynthesis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device for osteosynthesis shown in FIG. 1 to 5 consists of a boneplate 1 having a lower face 6 intended to rest against the bone, anupper face 5, as well as a passage 2 that connects the lower face 6 withthe upper face 5, to accommodate a multi-axially pivotable insert 10(FIGS. 2 and 4) for a bone screw 20 (FIG. 6), whereby the passage 2 hasa central axis 3. The insert 10 that can be inserted into the passage 2(FIGS. 2 and 4) possesses a central passage 11 for accommodating thebone screw 20 (FIG. 6), whereby the central passage 11 has alongitudinal axis 12, an outer sheath surface 13 that is intended forcontact with the passage 2, and an inner sheath surface 14 that definesthe central passage 11.

The insert 10 consists of a hexagonal helical spring, so that it isradially compressible and radially expandable. The passage 2 of the boneplate 1 has a radial narrowing 7 in cross-section towards the lower face6 and also towards the upper face 5, in order to prevent the insert 10from falling out or being pressed out. The narrowing 7 in cross-sectionof the passage 2 and the compressibility of the insert 10 arecoordinated with one another in such a manner that the insert 10 can beintroduced into the passage 2 in the compressed state.

As shown in FIG. 1, the passage 2 of the bone plate 1 is provided with amacrotexture in the form of grooves that run peripherally around thecircumference.

As shown in FIG. 3, the cross-section 4 of the passage 2, which standsorthogonal to the central axis 3, is approximately hexagonal, i.e.configured to be non-round. The cross-section of the insert 10, whichstands orthogonal to the longitudinal axis 12, has a shape essentiallycorresponding to the cross-section 4 of the passage 2 of the bone plate1, so that the insert 10 inserted in the passage 2 is fixed to preventrotation relative to its longitudinal axis 12, but remains partiallyaxially movable, i.e. pivotable, within the passage 2, relative to thebone plate 1.

As shown in FIG. 1, the diameter of the passage 4 narrows in thedirection of the lower face 6 of the bone plate 1, so that the passage 4is configured to be conical. Accordingly, the helical spring forming theinsert 10 is also configured to be conical.

The bone screw 20 shown in FIG. 6 can be inserted into the insert 10.The bone screw 20 possesses a threaded shaft 21 intended to be anchoredin the bone, a screw axis 23, as well as a screw head 20 intended forinsertion into the central passage 11 of the insert 10, whichessentially corresponds to the shape of the central passage 11. Thecross-section through the screw head 22, which stands orthogonal to thescrew axis 23, is narrowed towards the threaded shaft 21, so that a coneresults. The screw head 22 is provided with the outside thread 24, thepitch of which agrees with the pitch of the windings of the helicalspring implemented as the insert 10. Furthermore, the screw head 22possesses a hexagon socket 25 for accommodating an Allen wrench (notshown in the drawing).

In the following, the clinical use of the device for osteosynthesis willbe described briefly.

The insert 10 of the device is already pre-mounted in the passage 2 ofthe bone plate 1 or in another osteosynthesis device. Insertion by thesurgeon is therefore eliminated. The bone plate, with the inserts 10pre-mounted in the passages 2, is placed onto the bone. This can be doneeither before or also after repositioning of various bone fragments orvertebrae. To set the bone screws 20, there are three standardscenarios:

a) drill, cut a thread, screw in;

b) drill, screw in (with self-tapping screws); or

c) screw in (with self-drilling and self-tapping screws).

The use of target bushings or drill bushings is also possible. Ofcourse, the use of solid target bushings is not practical, because thiswould result in a loss of the advantage of a screw that can be adjustedin angle; however, such a target bushing could be useful in order tolimit the angle of adjustability. Drill bushings are used ifself-drilling screws are not used, and a hole has to be drilled first.In such a case, the drill bushing serves to protect soft tissue.

When several bone screws 20 are set, there are basically twopossibilities: a) in the case that repositioning takes place before thebone plate is applied, the bone screws 20 can be fixed in placeimmediately; and b) in the case that repositioning takes place after thebone plate has been applied, the bone screws 20 are only screwed in sofar, at first, that the bone plate is fixed in place on the bone; onlythen does final repositioning or correction take place, and the bonescrews 20 can be locked in place by means of turning them several angledegrees further.

While the present invention has been described with reference to thepreferred embodiments, those skilled in the art will recognize thatnumerous variations and modifications may be made without departing fromthe scope of the present invention. Accordingly, it should be clearlyunderstood that the embodiments of the invention described above are notintended as limitations on the scope of the invention, which is definedonly by the following claims.

The invention claimed is:
 1. A device for holding a bone fixationelement at a user selected angle, comprising: an osteosynthesis elementhaving a bone fixation element receiving opening defining a central axisextending therethrough; and a helical spring insert sized and shaped tobe mounted in the opening, a radial inner surface thereof defining anengaging surface for mounting a threaded head of a bone fixation elementtherein at any user selected angle relative to the central axis of theopening within a permitted range of angulation.
 2. The device of claim1, wherein the helical spring is non-round.
 3. The device of claim 2wherein the helical spring is prismatic.
 4. The device of claim 1,wherein the opening in the osteosynthesis element has a non-roundcross-section.
 5. The device of claim 4, wherein the opening in theosteosynthesis element has a prismatic cross-section.
 6. The device ofclaim 4, wherein a longitudinal cross-section of an outer surface of thehelical spring has substantially the same shape as the cross-section ofthe opening through the osteosynthesis element.
 7. The device of claim1, wherein the helical spring is one of radially compressible andexpandable.
 8. The device of claim 1, wherein the insert is fixed in theopening to prevent rotation thereof relative to a longitudinal axisthereof and configured and adapted to remain partially axially movablewithin the opening relative to the osteosynthesis element.
 9. The deviceof claim 1, wherein the cross-section of the opening in theosteosynthesis element is polygonal.
 10. The device of claim 9, whereinthe cross-section of the opening in the osteosynthesis element ishexagonal.
 11. The device of claim 1, wherein the opening is generallyprismatic.
 12. The device of claim 1, wherein the opening through theosteosynthesis element conically widens in at least one direction alongits central axis.
 13. The device of claim 1, wherein a central passageof the insert conically widens in at least one direction along alongitudinal axis thereof.
 14. The device of claim 1, wherein a centralpassage of the insert is generally prismatic.
 15. The device of claim 1,wherein a shape of a central passage of the insert is generallycylindrical.
 16. The device of claim 1, wherein at least one surface ofthe insert is roughened.
 17. The device of claim 1, wherein at least onesurface of the insert is coated with a harder material than the insert.18. The device of claim 1, wherein the opening through theosteosynthesis element is roughened.
 19. The device of claim 1, whereinthe opening through the osteosynthesis element is provided with acoating of a harder material than that of the osteosynthesis element.20. The device of claim 1, wherein the opening through theosteosynthesis element includes peripheral grooves that extend around acircumference of the opening.
 21. The device of claim 1, wherein theopening through the osteosynthesis element narrows in cross-section atfirst and second ends thereof to maintain the insert therein.
 22. Thedevice of claim 1, wherein an outer surface of the insert is convex. 23.The device of claim 1, wherein the opening through the osteosynthesiselement is concave.
 24. The device of claim 1, wherein theosteosynthesis element and the insert are formed of different materials.25. The device of claim 24, wherein the osteosynthesis element is formedof plastic and the insert is metallic.
 26. The device of claim 1,wherein the insert has a height measured along its longitudinal axisthat is smaller than a height of the opening through the osteosynthesiselement measured in the direction of its central axis.
 27. The device ofclaim 26, wherein the height of the insert ranges from 40% to 85% of theheight of the opening.
 28. The device of claim 1, further comprising abone screw having a threaded shaft for engagement of bone and a threadedhead sized and shaped for mounting in the central passage of the insertat an angle relative to the central axis thereof selected by a user. 29.The device of claim 1, wherein the osteosynthesis element is a boneplate.
 30. The device of claim 1, wherein the osteosynthesis element isone of a pedicle screw and a pedicle hook.
 31. The device of claim 1,wherein the osteosynthesis element is an external fixator.
 32. Thedevice of claim 1, wherein the osteosynthesis element is anintervertebral implant.
 33. The device of claim 28, wherein a pitch ofwindings of the helical spring corresponds to a pitch of an outsidethread of the screw head.
 34. A device for holding a bone fixationelement at a user selected angle, comprising: a bone plate having a bonefixation element receiving opening defining a central axis extendingtherethrough; and a helical spring insert sized and shaped to be mountedin the opening, a radial inner surface thereof defining an engagingsurface for mounting a threaded head of a bone fixation element at anysurgeon selected angle relative to the central axis of the openingwithin a permitted range of angulation, wherein the insert is configuredand adapted to be secured against rotation relative to a longitudinalaxis thereof while remaining pivotally adjustable relative to thecentral axis of the opening.
 35. The device of claim 34, wherein a shapeof the insert is substantially hexagonal.